Most automotive air bag restraint systems, presently in use, use gas generant compositions in which sodium azide is the principal fuel. Because of disadvantages with sodium azide, particularly instability in the presence of metallic impurities and toxicity, which presents a disposal problem for unfired gas generators, there is a desire to develop non-azide gas generant systems and a number of non-azide formulations have been proposed. However, to date, non-azide gas generants have not made significant commercial inroads.
U.S. Pat. No. 5,139,588, the teachings of which are incorporated herein by reference, describes gas generant compositions which use as fuel tetrazole and triazole compounds such as aminotetrazole, tetrazole, bitetrazole, 1,2,4-triazole-5-one, 3-nitro-1,2,4-triazole-5-one and metal salts thereof. The formulations further contain oxidizers, including alkaline and alkaline earth metal salts of nitrates, chlorates and perchlorates. This patent teaches that the cations of the fuel and oxidizer salts should include a mixture of alkaline and alkaline earth metal cations, whereby the salts formed during combustion include both liquid and solid salts that together form filterable clinkers. Furthermore, the compositions of this patent include materials such as silicon dioxide, boric oxide and vanadium pentoxide which reacts with corrosive oxides, such as potassium or sodium oxide, forming mixed metal salts.
It is noted in U.S. Pat. No. 5,139,588 that the compositions are useful in aspirator systems. These systems, which are generally no longer used, were typically made of steel. Space, cost and weight requirements of the present day automotive industry generally require small aluminum units in which the gas is provided entirely by the gas generant, not by venturi action in conjunction with gas generation. While an aluminum housing and other aluminum components have the advantages of being lightweight and easily machined, and therefore inexpensive to produce, aluminum has the disadvantage of being a highly reactive metal, e.g., as compared to steel. In particular, aluminum is rapidly degraded by alkali metal oxides such as Na.sub.2 O and K.sub.2 O, particularly at high temperatures. Gas generant compositions based on azoles, as in the U.S. Pat. No. 5,139,588, burn at much higher temperatures than do sodium azide-based gas generant compositions. Accordingly, the problem of degradation of aluminum by alkali metal oxides is exacerbated. There is a need for gas generant compositions to be used in conjunction with aluminum component-containing gas generant systems in which alkali metal oxides are more efficiently scavenged.
U.S. Pat. No. 5,139,588 furthermore describes the formation of pellets of the compositions by compression molding. If pellets are the form of gas generant composition to be utilized, as is frequently the case, the pellets must remain in that form over an extended period of time, during which the pellets will be subject to frequent vibration and other mechanical shocks. It is not believed that azole-based pellets, formed by compression molding, without a binder, would exist in that form for long when the gas generant module is employed in a vehicle and subject to jarring and vibration.